In the art of making tires, it is desirable to employ rubber vulcanizates that demonstrate reduced hysteresis loss, i.e., less loss of mechanical energy to heat. Hysteresis loss is often attributed to polymer free ends within the cross-linked rubber network, as well as the disassociation of filler agglomerates.
Functionalized polymers have been employed to reduce hysteresis loss and increase bound rubber. The functional group of the functionalized polymer is believed to reduce the number of polymer free ends. Also, the interaction between the functional group and the filler particles reduces filler agglomeration, which thereby reduces hysteretic losses attributable to the disassociation of filler agglomerates (i.e. Payne effect).
Selection of certain functionalized anionic-polymerization initiators can provide a polymer product having functionality at the head of the polymer chain. A functional group can also be attached to the tail end of an anionically polymerized polymer by terminating a living polymer with a functionalized compound.
Conjugated diene monomers are often anionically polymerized by using organometallic compounds as initiators. Exemplary organometallics that are well-known as anionic-polymerization initiators for diene monomers, with and without monovinyl aromatic monomers, include alkyllithium, trialkyltin lithium, and certain aminolithium compounds. The synthesis of lithiodithiane reagents is known as is there addition to conjugated ketones. However, no use of sulfur containing initiators, particularly lithium thio acetal based compounds, is known for anionic polymerization of dienes, trienes, monovinyl aromatics or combinations thereof.
Because functionalized polymers are advantageous, especially in the preparation of tire compositions, there exists a need for additional functionalized polymers. Moreover, because precipitated silica has been increasingly used as a reinforcing particulate filler in tires, functionalized elastomers having an affinity to both carbon black and silica fillers are needed.